In BJJ, how important is sparring?

Sparring (rolling) is where you learn the practical application of your technique. There's no way to quantify "how much better" you'd be (I dunno, five grappling points better? 37 XP closer to LV 1?) but you will improve faster if you spar more. In addition, I'd suggest sparring with a specific goal in mind, like looking for a Kimura or defending mount, as well as asking your sparring partners for feedback. Martial arts is as much an intellectual pursuit as a physical one, so keep your mind working.